Rich of Peak (ROP) vs Lean of Peak (LOP)/Engine operation

[KyleTownsend]

TGresham makes excellent points supporting LOP operation. My own analysis came up with similar results (I think I figures 7.50 per gallon). However, at my rate of usage, it would take 10 to 15 years to reach TBO, and my payback period would have been well over 5 years. This is a longer payback period than I was comfortable with. But, that is a personal choice.

On the other hand, if I can reach a comfort level that the purchase of an expensive engine analyzer is going to pay for itself within that time frame due to extended engine life or maintenance savings, the purchase decision becomes easier.

[KyleTownsend]

I appreciate Walter's comments.

On the subject of whether the manufacturers established a "design point" to help "idiot-proof" engine operations, or whether they were unduly influenced by the marketing department is certainly a fun topic for debate. I too am skeptical of the marketing guys, and nothing they did would surprise me.

On the other hand, their reasons have nothing to do with the science of this issue, and speculating on their reasons does tend to make the issue more emotionally charged.

I freely admit that I am pretty new to this issue, and am here to learn from those of you that know a lot more about it than I do. I am just trying to make sure I understand the facts and don't tear up my airplane.

Let's examine the premise that is it OK to operate the engines according to the manufacturers recommendations. I am already convinced that this is not optimal from an effeciency standpoint. Alas, right now, I really can't afford to properly instrument my engine and get GAMI injectors, so for some period of time, I am going to have to continue operating the plane with nothing more than the factory supplied instrumentation and the optional single-probe factory EGT. Under those circumstances, I want to answer the following questions:

1. Is it OK to follow the POH recommendations. My POH says:
a. operate at 75 percent power or less in cruise flight.
b. operate 50 degrees rich of peak egt when at 65-75% power.
c. operate at peak cht at 65% power or less.

As far as I can tell, no one is disputing that (c) is OK, so let's focus on (b) at 75% power (If anybody is disputing this, please say so).

Walter indicates that this 50 ROP EGT setting is between peak CHT (40 ROP EGT) and best power (80 ROP EGT) based on the tests that they have done. Based on the GAMI charts that I have seen in George's Braley's articles, the CHT's are within 10 degrees of those found at best power. With the instrumentation that I have, my margin of imprecision is high enough that, for all practical purposes, this setting is equivilant to both best power and peak cht (probably some cylinders will be at one, and other cylinders at another).

In order to REALLY know if this setting is OK, I would need to know if the CHT's for each cylinder are running below 400 degrees. If they are, I'm OK, and if they are not, I am running too hot (again, if there is any disputing this point, please say so).

Unfortunately, this is a catch 22. I can't know this with certainty without an engine monitor. So, we are reduced to asking, is this OK IF the engine is functioning properly.

If the engine is functioning properly, then the cylinder with the CHT probe should be the hottest running cylinder, by design. THIS IS A MAJOR ASSUMPTION. Perhaps those of you with engine monitors on the skymaster can answer this question. If it is not the hottest cylinder, then the temperature limit would have to be adjusted down to some extent. By analyzing the data of those of you have engine monitors, we could answer the question "how much."

2. Irregardless of the answer to question 1, is there a better way to operate these engines IF you don't have an engine analyzer.

3. I think a large percentage of us use no more than 65% power in cruise (perhaps because of economy, or concerns about engine wear, or both). Is there any reason to not do this? Does it add enough of a "margin of error" that it becomes extremely unlikely that we will damage the engine no matter what we do with the mixture control?

[Walter Atkinson]

Kyle:

Yep. My position is that GAMI's can save you money....... but, an engine monitor can save your life. The engine monitor is much more important and GAMI will tell you the same thing. If you can only afford one or the other, the people at GAMI will strongly suggest that you get the engine monitor. That speaks well of their integrity in my view.

Here's the problem.

As soon as an owner installs an engine monitor and find out how crummy his F:A ratios are--even ROP--many folks get the GAMIjectors so their engine will run like it should have been running in the first place.

Oh, well, such is life. <g>

[KyleTownsend]

WOOPS! In my previous post, item (c) should have said "operate at peak EGT" not "operate at peak CHT".

Now, on to my real question.

I don't actually think that the LOP guys and the manufacturers are as far apart as they appear. They certainly aren't that far apart on their data.

Taking the manufacturers "side" for a moment, I believe that we all agree that:

(1) at the time most of these airplanes were built, multi-probe engine monitors were either not available or were prohibitively expensive (they are still pretty expensive); and

(2) without these engine monitors, there is no better alternative than following the manufacturers recommended power and mixture settings, provided we keep an eye on the CHT's (by running them at 400 degrees or less).

Now, here is the part that I "don't get." Cessna has the charts, GAMI has the (even better) charts. If I am reading them correctly, then operating by the manufacturers settings at 75% power leads to the highest possible CHT's for that power setting. They just aren't going to get any higher, no matter what you do (o, if you want to split hairs, they can't get more than a few degrees higher, since true peak CHT is more like 40 DROP EGT).

If this is true, and if "everybody" knows that operating at peak EGT is actually going to be cooler than operating at 50 DROP, then why does the POH say you shouldn't lean to peak EGT above 65% power?

Correct me if I am wrong, but I can's see anything wrong with setting MP and RPM for 75% power, then leaning to peak egt and leaving it there (instead of enrichening to 50 DROP).

Extending this argument further, I don't see any reason that I couldn't continue to lean the engine until I was running at 50 DLOP (assuming that the engine would run smoothly at this point, which it probably wouldn't without gami's).

But for argument's sake, lets say I have GAMI's but my engine monitor died or whatever, so I'm having to rely on the factory gauges.

I absolutely don't see how this would hurt anything.

Of course, the "catch" is, that if I leaned to peak EGT, or leaner, then I would not still be making 75% power. I would be making some lesser amount. But if I am OK with making this lesser amount of power, I really don't see how this could possibly hurt anything.

And this is where I guess the "kicker" is. In order to perform LOP operations AT HIGHER POWER SETTINGS (I am guessing settings where the real power exceeds around 65 to 70 percent), it is necessary to move the manifold pressure and/or RPM controls to a position HIGHER than the factory recommended settings for 75% power operation (the "power recovery" step).

If I do this (eg: by advancing MP until the airspeed is what it was before I started leaning) and I DON'T have an engine monitor, then it is possible that an individual cylinder could be running at some power setting greater than "book 75%" because of unbalanced fuel flows.

So, I can see why this would be a no-no.

However, I can't see why I shouldn't lean as much as I want to from the factory 75% setting, provided that I don't do the "power recovery" step.

Am I thinking right, or not?

[Walter Atkinson]

Kyle:

It seems to me that you're gaining a pretty good hold on the concepts. Some points to further your understanding:

**I don't actually think that the LOP guys and the manufacturers are as far apart as they appear. They certainly aren't that far apart on their data.**

Actually, there is no argument at all on the data. None. Period. It all agrees 100% because, as Sir Isaac Newton said, "The physics are everywhere the same."

**(2) without these engine monitors, there is no better alternative than following the manufacturers recommended power and mixture settings, provided we keep an eye on the CHT's (by running them at 400 degrees or less).**

That's close, but not altogether precise. Keeping CHT's below 400 is a good guide but it does not address ICPs completely, but it's difficult to be too argumentative with that statement. It's pretty close.

You comments about the charts are correct. The Cessna and GAMI charts are in agreement because the physics are, indeed, everywhere the same.

**If this is true, and if "everybody" knows that operating at peak EGT is actually going to be cooler than operating at 50 DROP, then why does the POH say you shouldn't lean to peak EGT above 65% power?**

Because an engineer didn't write the POH! I, too, would like to see a scientific explanation for that statement. I know of none. OTOH, be aware that the common recommendation not to lean above 75% power is an attempt to keep the pilot from operating inside what we later termed the Red Box. It was an admonition by the OEM that assumed that the pilot was not knowledgeable and had little instrumentation--which in many cases isn't all that bad of an assumption!

**Correct me if I am wrong, but I can's see anything wrong with setting MP and RPM for 75% power, then leaning to peak egt and leaving it there (instead of enrichening to 50 DROP).**

Our research indicates that peak EGT is not quite lean enough at 75% power to keep the ICPs low enough to be in harmony with longevity concerns. You are absolutely correct that it is a better choice than 50dF ROP. I'd say peak is "less bad" at 75% power. <g>

**Extending this argument further, I don't see any reason that I couldn't continue to lean the engine until I was running at 50 DLOP (assuming that the engine would run smoothly at this point, which it probably wouldn't without gami's).**

That is 100% in harmony with all of the known physics.

**I absolutely don't see how this would hurt anything.**

It won't. It's actually better.

**And this is where I guess the "kicker" is. In order to perform LOP operations AT HIGHER POWER SETTINGS (I am guessing settings where the real power exceeds around 65 to 70 percent), it is necessary to move the manifold pressure and/or RPM controls to a position HIGHER than the factory recommended settings for 75% power operation (the "power recovery" step).**

Correct. You have to get the mass airflow up so you can put the fuel to it. I currently, routinely operate at about 60dF LOP, 85-90% power in cruise. The engine loves it..... and I go faster on lower FF than if I were making 75% power ROP.

**If I do this (eg: by advancing MP until the airspeed is what it was before I started leaning) and I DON'T have an engine monitor, then it is possible that an individual cylinder could be running at some power setting greater than "book 75%" because of unbalanced fuel flows.**

Right... but... if it's running smooth LOP, it MUST have balanced FFs. <g> In that case, you don't need an engine monitor to run LOP.

Duzzat make sense? <g>

[KyleTownsend]

Walter:

Yes. This clears up a lot of the questions that I had.

The one thing that I hadn't realized is that your research indicates that operating 50 degrees rich of peak egt at 75% power, per the manufacturers recommendations, actually causes the engines to run in the "red box" because the ICP's are at some level that is objectively "bad"?

Am I understanding you correctly on this one?

[Walter Atkinson]

Kyle:

You understand that correctly. To keep ICPs under control at 75% power you need to be richer than about 125dF ROP or leaner than about 20dF LOP. Doing so is beneficial to longevity. The Red box grows as power increases and it shrinks as power decreases until it no longer exists somewhere between 60 and 65% power. To follow the science, you must either allow range to suffer or be able to run LOP at power settings above 60-65%. That's why the manufacturer's recommended cruise power settings are as low as they are.

The Manufacturer's MARKETING Department's recommendations of 50dF ROP at 75% power are not, in our view, a good idea based on the observations we have made over many hunderds of hours of test cell work and the field observations. If longevity is not an issue, then 25-50dF ROP is the mixture setting that will result in the best trade-off between airspeed and range--just like the Marketing Department suggests.

Those who have been operating at high powers LOP have been getting excellent results because range and speed are both better while keeping ICPs controlled for increased longevity. I routinely run between 85 and 90% power in cruise with a cool engine and good range. My engine is pristine clean with no buildup of anything on the pistons, or valves. The oil stays clear for 20-25 hours. You can acheive the same longevity with very rich mixtures, but the engine will run a lot dirtier. ROP is OK if you are rich enough. It will result in higher maintenance since it will have much more deposits in the combustion chamber and the oil will get dirtier quicker. I donlt have any hard data, but it makes sense that clean oil is better than dirty oil.

According to Carl Goulet, former VP of Engineering at TCM, "Cooler is better. Cleaner is better. LOP is cooler and cleaner." His position is certainly in harmony with the science as we have observed it. <g>

Regards,

[Walter Atkinson]

Kyle:

In answer to your questions, this was posted on the Cessna board this morning. It speaks directly to the points we are discussing. He's flying a CARBURETED 182. Notice that he's flying faster, cooler and on less fuel! This is a common response.

Walter

*****

Flew Santa Barbara (SBA) to John Wayne (SNA) at 5500'. Started with 7 degrees C carb temp, WOT, 2425 RPM, 10.3 GPH. Got 25-30 LOP. 76% HP. Hottest CHT was 329 with cowl flaps closed. I'm usually up around 16 GPH 200 ROP to get 75% power. Normally I fly 65% power at 25 ROP. I gained a few knots IAS today and burned a bit less gas. Very cool .
I strongly encourage everyone to attend the APS course. It's fun, informative and worth every cent. It is so nice to have the entire power/mixture spectrum available.

Thanks Walter and George.

Randy

[KyleTownsend]

Walter,

Thanks for taking the time to answer my questions.

As you know from following the thread, I am "sold" on the LOP concept provided that one has an engine monitor, particularly in terms of effeciency. I've looked at the data, and it says what it says.

Also, Continental's new FADEC system runs LOP I understand, and I guess they wouldn't do that if it was going to tear up the engine. This gives me some additional comfort.

On the subject of ICP's, I still don't have a firm understanding of how much is too much. I understand that it varies with crank angle, and in any event, I'm not going to be able to measure this directly.

Right now, I don't have an engine monitor, and I've already blown this year's "goody budget" on a new GNS480 (hopefully installed in 2 weeks).

So, for at least the next year, I'm going to have to run with what I've got. My main concern is not doing any damage to the engines in the mean time.

Heretofore, it has been my practice to take off at full power, reduce to 75% power at about 500-1000 AGL (with everything at the top of the green including fuel flow), and cruise at "65% power" and peak EGT (which would actually be somewhat less than 65% power, really). I generally use the cruise power (and mixture) setting in my initial descent, and gradually reduce power so that I am at approach speed when I level out (assuming I am going to be at the IAF at that time). This gradually cools the CHT's.

I suppose the main thing that I need to verify at this point is whether the "top of the green" fuel flow used in climb is at least 125 degrees rich of peak EGT.

If so, then my operating practices should be OK (provided of course that I keep the CHT under 400).

If there is not a 125 ROP margin in my climb power setting, then I need to enrichen enough in the climb to get 125 degree temperature margin.

Is this correct?

Is this a reasonable and conservative way to operate until I get all the goodies?

Thanks,

Kyle

PS: I recently read an article by Mike Busch over at CPA. He endorsed LOP operations in his article.

[kevin]

Kyle,

Walter and others will certainly express their opinion, but in my view, and in the view of the very knowledgeable turbocharged piston engine mechanic that used to work on my P, there is no reason to pull the mixture lever back at all during climb. Reduce to the climb power setting that Cessna specifies, but then leave the mixture in. You will burn a bit more fuel, but will reduce the risk of hurting your engine. Depending on the fuel flow gauge is not a good idea. They can go out of calibration very quickly, and you could fry your engine fast.

I will be interested in Walter's reply to the concept of running at peak EGT and 65% in cruise. I have previously been told that this is not a good idea, because (with GAMIs) fuel distribution to the cylinders is uneven, and you could end up with one or more cylinders inside that red box he talks about, even though you have leaned to peak based on your Cessna (I guess that is what you are using) EGT guage. I've also been told that at 65%, you can run it anywhere up to and including peak, and it won't hurt it, so it would seem that what you suggest would be OK.

But anyway, my only point was that pulling back the mixture to the top of the green is not the best practice, in my view. I ran my P337 the way I describe for several years. It simplified operation, used a little fuel for cooling, and gave me a bit more peace of mind. I did this even when I had an analyzer, because leaning for climb with an analyzer (in an IFR step climb for example) seemed like a pain.

Kevin

[Kevin McDonnell]

Kevin,

What you're suggesting (leaving the FF extra rich during the cruise climb) is something Walter advocates - and told me I too would be convinced as to why this is a good idea by attending the class. Let me tell you, he delivered on that promise.

I now leave the mixtures full rich during cruise climb to make the cylinders run much cooler and to increase the detonation margin. This equates to about 19 to 20 gph for cruise climb vs. the book recommendation of 15 gph. Let’s say you climb to 7,500 feet at 500 fpm – that’s only 2.5 gallons extra. Even climbing to 15K’ will only cost an extra 5 gallons of “excess” burn. That’s pretty small considering our tank sizes. Previously, I used to have to carefully monitor CHT's in the climb and tweak airspeed and mixture to keep them under control. That is simply a thing of the past.

Regarding your other point about running at peak when at 65% power, GAMIs don't make this worse - but in fact make it better. By definition, peak is the point at which the maximum EGT is achieved. And richer or leaner will result in a cooler EGT. With the Cessna gage, when one cylinder reaches peak, you have no evidence where the other 5 are - they might be leaner, or they might be richer. GAMIs are tuned so that all cylinders peak at virtually the same fuel flow. That means when one of the peaks, they are all very close to the same point - much closer than if you weren't using GAMIs. That said, at 65% power, I don’t think the red box exists.

The uneven fuel distribution (while true) is a red herring. The reason for this is the design of the engine resulted in uneven air flows to the cylinders. In order to reach the optimal fuel air mixture, the GAMIs match the fuel flow to the engine’s uneven airflows. If all cylinders are at the optimal mixture, then they will all peak at the same fuel flow.

[Walter Atkinson]

Kyle and Kevin:

Good questions.

1) The data suggests that Kevin is right about not pulling the mixture back on the TC'd engine in the climb. You will find much cooler CHTs during the climb if you do not pull the mixture back. Leave it rich. This is very helpful during the time that you have very poor cooling from low airflow. It will cost you about one gallon total during the climb.

This is different than the NA engines where we recommend leaning to a Target EGT in the climb. Remember, as far as MP is concerned, your engine always thinks it's at sea level. Keep it sea level rich!

2) At 65%, you can play fooseball with the mixture and not hurt anything. Set it anywhere you like as long as the CHTs remain under 380dF.

3) The presence of poor F:A ratios is costing you performance and options. If I owned a turbo Skymaster, I would want to get the F:A ratios balanced so I could use the advantage of the turbo and go FAST. I could operate those engines at much higher power settings in cruise on low FF and go fast while keeping the CHTs cool. That's how we operate the big TCM engines and they do quite well like that.

4) You are giving up only about 2 knots from best power while operating at peak. You save a bunch of fuel. CHT's at peak are almost exactly the same as best power CHTs. Sounds like a good idea to me if it will stay cool.

5) IF it will run smooth LOP, it means that the F:A ratios are balanced and in that case, there is absolutely no reason not to run it LOP--even without an engine monitor. Again, the real reason to have an engine monitor has little to do with ROP/LOP choices. You REALLY need and engine monitor if you run ROP, not LOP. The data on this is very compelling once you see it.

[Guy Paris]

Walter..
My GAMI's are enroute..

**This is different than the NA engines where we recommend leaning to a Target EGT in the climb.

Just curious Walt, what will the target EGT be in climb? My mechanic at one time suggested to leave the throttles at the take off position till reducing for cruise for the full throttle inrichment. (good idea or no). On my JPI I notice the increase of EGT's if I reduce to a climb power setting. guy, the old 72 driver...

[Walter Atkinson]

Guy:

**Just curious Walt, what will the target EGT be in climb?**

That changes from engine to engine, but a very good starting point is 1275-1300dF on most of the NA engines we're dealing with. Pick the hottest EGT and keep it in that range and it will pay dividends in climb rate and fuel savings. That should work fine.

** My mechanic at one time suggested to leave the throttles at the take off position till reducing for cruise for the full throttle inrichment. (good idea or no). **

You have a knowledgeable mechanic. That's excellent advice which is compatible with the science. I have one question. Why reduce MP at cruise? You're NA, right? Leave it WOT in cruise and GO!

**On my JPI I notice the increase of EGT's if I reduce to a climb power setting. **

Yes, this is from the change in the effective timing that results from the changes in MP and rpm. Take your mechanic's advise and leave it WOT and only reduce rpms after takeoff if there is a noise abatement or POH limitation issue. Your engine will run under less stress that way. Seems counter-intuitive, but it's true. The way they are engineered, there is less stress on the engine at WOT and full rpms than with the MP and RPM reduced for climb power. Sounds crazy, but that's the MEASURED reality.

[KyleTownsend]

Incorporated the "full rich climb" into my SOP's today. Seemed to work fine. Thanks Kevin, et. al.

Of course, now that I am actually paying a lot more attention to all of this stuff, I am beginning to wonder if I can trust my factory gauges at all. I flew a 3 1/2 hour out and back today, and CHT's never got over 300 degrees (as far as I could guess with the factory gauge). Also, oil temps never even got close to 180, which I understand is about the level needed to "boil off" any moisture in the oil. ARGH! It sure would be nice to have gauges I know I can count on (I know, buy a JPI).

The last couple of posts raised another question for me. Am I understanding that it is OK to climb at WOT and Full rich but to pull the RPMs back? I would have thought that this would shift the peak of the combustion event closer to TDC. Isn't this what we are trying to avoid?

Kyle